Houston: Several American aid workers, exposed to Ebola in Sierra Leone, have been flown back to the US where health authorities will watch them closely for symptoms of the disease, authorities have said.

Some exposed workers are due to arrive back in the US today and will be quarantined near special isolation units, according to the Centers for Disease Control and Prevention.

Partners in Health, a nonprofit group with 2,000 staff in West Africa, said the Americans are being evacuated and quarantined out of an abundance of caution.

Earlier on Saturday the Centers for Disease Control and Prevention said several people would be flown to the US by private jet.

"Ten clinicians who came to the aid of their ailing colleague were subsequently identified as contacts of the evacuated clinician," Partners in Health said in a statement on its website.

None has any symptoms.

Meanwhile, the number of people killed by the Ebola virus disease (EVD) has reached 9,976, the World Health Organisation (WHO) said in a report on Wednesday.

A total of 24,282 cases of the Ebola virus disease have been reported.